Sensors for detecting position and displacement are often used in many mechanical processes in which it is important to position and/or move a ram, or the like, axially under precise control. It is well known in the art that signals containing information related to the position and displacement of a moving ram can be generated by mounting transducers in close proximity to the ram and outfitting the ram with equally-spaced magnetic bands disposed circumferentially around the girth of the ram. It is common for such systems to employ two transducers mounted in close proximity to the ram such that when the ram moves, the bands of magnetic material pass by the transducers thereby generating sinusoidal output voltages at the transducers. Traditionally, the two transducers are positioned precisely in respect to each other such that the two sinusoidal output signals are in quadrature (i.e., the transducer output signals are 90 degrees out of phase). Conversion of the two sinusoidal signals in quadrature into corresponding digital pulse trains, wherein each pulse corresponds to the passage of a magnetic band, yields meaningful information related to the position and displacement of the ram. Each pulse train changes state twice, once for each time the corresponding sinusoidal output signal crosses zero, over one period from one magnetic band to the next. Due to the fact that the pulse trains are 90 degrees out of phase, four state changes occur per period. It is well known in the art that the pattern of the state changes of the pulse trains reveals information related to the position and displacement of the ram. However, because there are only four discernible state changes per period, the resolution of such systems is limited and often proves inadequate.
Numerous systems and techniques for enhancing the resolution of conventional quadrature position and displacement sensors are known. However, these systems and techniques are plagued by a number of infirmities. For instance, many known systems for enhancing resolution require long chains of costly analog electronic circuitry. In addition to increasing cost, the elaborate analog circuitry required by such systems increases the systems' sensitivity to electromagnetic noise, distortion, and other environmental disturbances. Furthermore, many known systems for enhancing resolution often require the size and the complexity of the circuitry to scale proportionately with the desired increase in resolution. In other words, in order to double the resolution of the system, it is necessary to double the size and complexity of the circuitry. Moreover, a number of known systems for enhancing resolution cannot handle changes in the amplitude of the transducer output signals and consequently require manual calibration of analog circuit components like potentiometers. Finally, numerous known systems rely on lengthy, difficult, and costly digital operations such as digital division operations.
There is therefore a need in the art for a simple and efficient method and system of sensing the position and displacement of a moving substrate, ram or the like that provides, among other things, enhanced resolution and is capable of self-calibration.